In the fabrication process for a semiconductor device, numerous processing steps must be performed on a semi-conducting substrate to form various circuits. The process may consist of as many as several hundred processing steps. Each processing step is executed in a process chamber such as an etcher, a physical vapor deposition chamber (PVD), a chemical vapor deposition chamber, etc.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum, a gas plasma or other chemical environment must be provided for the process. For instance, in a PVD (or sputter) chamber, a high vacuum environment must first be provided that surrounds the wafer such that particles sputtered from a metal target can travel to and deposit on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition chamber (PECVD), a plasma cloud of a reactant gas or gases is formed over a wafer positioned in a chamber such that deposition of a chemical substance can occur on the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer therefore is normally conducted in a hermetically sealed environment that is completely isolated from the atmosphere. Numerous processing equipment has been provided for such purpose. One of such widely used cluster-type fabrication equipment is marketed by the Applied Materials Corporation of Santa Clara, Calif., i.e., the Centura.RTM. 5000 system.
In a typical Centura.RTM. 5000 cluster-type wafer handling system, as shown in FIG. 1, the basic system 10 consists of two independent vacuum cassette load-locks 12 and 14, a capacity for one to four independent process chambers (two of such chambers 16 and 18 are shown in FIG. 1), a capacity for two service chambers which includes an orienter 22, and a vacuum transfer chamber 20 which is isolated from vacuum cassette load locks 12, 14 and process chambers 16, 18 by slit valves (not shown). The modular design of the basic system 10 is such that up to three high-temperature deposition chambers may be installed in the system. The basic system 10 can be used for fully automatic high-throughput processing of wafers by utilizing a magnetically coupled robot. The basic system 10 is further capable of transferring wafers which are maintained at a temperature as high as 700.degree. C. The basic system 10 also allows cross-chamber pressure equalization and through-the-wall factory installation. The vacuum pumps for the process chambers 16, 18, the transfer chamber 20 and the cassette load-locks 12, 14 are mounted at a remote location to prevent mechanical vibration from affecting the operation of the system.
The vacuum cassette load-locks 12, 14, the process chambers 16, 18 and the orienter 22 are bolted to the vacuum transfer chamber 20 and are self-aligned for ease of expansion or modification. Each of the process chambers 16, 18 is capable of processing a single wafer for achieving wafer-to-wafer repeatability and control. The temperatures in the process chambers 16, 18 are controlled in a closed-loop circuit for accuracy.
A plane view of the basic system 10 of FIG. 1 is shown in FIG. 2. In the basic wafer processing system 10 shown in FIGS. 1 and 2, the transporting of wafers between the various load-lock chambers 12, 14, the process chambers 16, 18 and the orienter 22 must be carefully conducted to avoid damages from occurring to the wafers. To accomplish such task, the wafer is transported by a wafer transfer system 24. The wafer transfer system 24 consists mainly of a robotic handler which handles all wafer transfers by a single, planar, two-axis, random access, cassette-to-cassette motion. A magnetically coupled robot permits good vacuum integrity and service without interrupting chamber integrity. The major component of the wafer transfer system 24 is a robot blade 28. The robot blade 28 permits high-temperature transfer of wafers without incurring contamination. A non-contact optical wafer centering process is also performed during the wafer transfer process. A constant flow of filtered inert gas such as nitrogen is used in the cassette load-locks 12, 14 and the vacuum transfer chamber 20. A conventional robot blade 28 can be fabricated of a non-magnetic type metal such as aluminum.
One of the process chambers 16, 18 is frequently used as an etch chamber for performing an etching process on a wafer. For instance, when the formation of alignment marks on the surface of a wafer is necessary, an etching process utilizing a corrosive gas is used for etching the marks (or holes) in the wafer surface. The surface layer etched may be a polysilicon layer. After he completion of the etching process, the robot blade 28 transfers the etched wafer from the etch chamber back into one of the load-lock chambers 12, 14. When such direct transfer of wafers between an etch chamber and a load-lock chamber occurs, a small amount of residual corrosive gas that was left on the surface of the wafer is frequently carried into the load-lock chamber. While the amount of residual corrosive gas left on a single wafer does not present a corrosive problem to a load-lock chamber, the total amount of corrosive gas carried by as many as 25 wafers stored in a wafer cassette situated in the load-lock chamber produces a cumulative effect and causes a serious corrosion problem on the components in the load-lock chamber.
Most components in a load-lock chamber are fabricated of metal which is susceptible to corrosion by an etching gas such as Cl.sub.2 or F. For instance, the components include a stainless steel bellow which is constructed in a corrugated structure and thus any result of corrosion such as holes formed through the bellow is difficult to detect. Other components such as an aluminum base used in the load-lock chamber is also subjected to the corrosive effect of Cl.sub.2 or F. A SMIF arm made of metal that reaches into the load-lock chamber for loading or unloading a wafer and various metal fasteners used on the arm are also subjected to corrosion when contacted frequently by the corrosive gases.
It is therefore an object of the present invention to provide a method for preventing corrosion in a load-lock chamber used in a cluster-type wafer fabrication system that does not have the drawbacks or shortcomings of the conventional method.
It is another object of the present invention to provide a method for preventing corrosion in a load-lock chamber incorporated in a cluster-type wafer fabrication system by adding an additional degas chamber to the fabrication system.
It is a further object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system by first transferring an etched wafer to a degas chamber prior to transferring of the wafer back into the load-lock chamber.
It is another further object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system when wafers are processed in an etch chamber by corrosive gases such as Cl.sub.2 or F.
It is still another object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system by purging a surface of an etched wafer in a degas chamber by a purge gas of N.sub.2 or O.sub.2.
It is yet another object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system by purging a surface of the wafer in a degas chamber with a purge gas at a flow rate between about 100 sccm and about 5,000 sccm.
It is still another further object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system by purging the surface of an etched wafer with a purge gas until substantially all residual corrosive gas has been removed from the surface of the wafer.
It is yet another further object of the present invention to provide a method for preventing corrosion in a load-lock chamber that is used in a cluster-type wafer fabrication system by purging the surface of a processed wafer with a purge gas of either N.sub.2 or O.sub.2 for a length of time of about 30 seconds to substantially remove all residual corrosive gas from the wafer.